Firefox OS App Tutorial
Creating a Project

At First create a folder to keep your project files in togather. In the folder first create a manifest.webapp file. Then write the descriptions of the app in the file as shown in the image.

Then create an index.html file and then create necessary html and css file for your app. Add js on the html file or add external js script for your app. After creating all your project files you then can run the app in the firefox os simulator.